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|  |  | Estuarine Science Salt Wedge Estuary Salt wedge estuaries occur when the mouth of a river flows directly into salt water. The circulation is controlled by the river that pushes back the seawater. This creates a sharp boundary that separates an upper less salty layer from an intruding wedge-shaped salty bottom layer. The mouths of the Mississippi, Columbia and Hudson rivers are examples of salt wedge estuaries. 
  
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